Automatic ionic fire alarm system



March 10, 1970 NAGAO ABE AUTOMATIC IONIC FIRE ALARM SYSTEM File d Aug. 18, 1966 United States Patent 3,500,368 AUTOMATIC IONIC FIRE ALARM SYSTEM Nagao Abe, Chofu-shi, Japan, assignor to Nittan Company Limited, Tokyo, Japan Filed Aug. 18, 1966, Ser. No. 573,284

Claims priority, application Japan, Mar. 30, 1966,

Int. Cl. G08b 17/10 US. Cl. 340237 7 Claims ABSTRACT OF THE DISCLOSURE An automatic fire detecting device comprising a housing with openings communicating with the atmosphere, a dividing means within the housing for dividing the housing into an atmospheric isolated inner ion chamber and an outer ion chamber, the latter communicating with the atmosphere and isolated from the inner chamber, the dividing means including an electrode cover having an inner and outer surface communicating with the inner and outer ion chambers, respectively, an inner radioactive source disposed on the inner surface and an outer radioactive source disposed on the outer surface, an inner electrode means disposed in the inner ion chamber in spaced relationship from the inner radioactive source, and an outer electrode means disposed in the outer ion chamber spaced from the outer radioactive source, the inner and outer radioactive ources emitting radioactive rays toward the inner and outer electrode means, respectively, and circuit means for comparing the ionization conditions of the inner and outer chambers and detecting any difference therebetween caused by smoke entering the outer ion chamber, including a field effect transistor, and a constant voltage diode for conducting in response thereto and a controlling rectifier responsive to the latter.

The present invention relates to a fire alarm device using an ion system which operates in response to smoke, containing inflammable particles, generated in the initial period of a fire.

It is one object of the present invention to provide an eflicient automatic fire alarm device of minimum size and particularly having a detecting device which detects smoke at the initial phases of a fire and which utilizes a low operating voltage, which employs a minimum of radioactive substances.

Conventional fire alarm devices are known which detect smoke by using radioactive rays. However, the conventional devices are complicated in construction and expensive. In addition the operation is inaccurate due to a construction in which the central part of the connection between two series arranged ion chambers each having a separate radioactive source is connected to a control electrode or grid of a relay tube. One ion chamber completely surrounds the other and the outer chamber communicates with the ambient air. The electrode or grid potential of the relay tube is changed by changes in the air constituents, and at the same time, an ionic current comprising a one-sided potential is developed on a certain block of the ion chamber.

Furthermore, due to the complex ion chamber of the conventional types, the production procedure and expenses for manufacture thereof becomes very expensive. Also, precise measuring and detecting of the smoke cannot be expected. In addition, the glass body of the relay tube which is built into the ion chamber, is aflixed by an adhesive material. Further, the glass of the tube is fixed to the disc by the use of a special metal alloy.

It is one object of the present invention to provide a fire alarm device having improved mechanical effects, and

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using a very small amount of radioactive source, and one which is very compact, efiicient and reliable.

It is another object of the present invention to provide an automatic fire detecting device in which respective radioactive sources are provided on both outer and inner surfaces of an electrode cover by forming two ion chambers, an outer ion chamber and an inner ion chamber, and on these ion chambers, the corresponding electrodes are disposed and the outer ion chamber freely communicates with the outer atmosphere. A constant voltage diode is provided which allows operation of a regulating rectifier for passing current to actuate an alarm and a comparator means compares ionization conditions in the inner and outer chambers and includes a field effect transistor which become conductive upon a change of voltage due to a change of conditions in the outer chamber and which allow operation of the constant voltage diode after detection of changes of the ions appearing in the ion chambers.

With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawing, in which:

FIGURE 1 is a perspective view of one embodiment of the present invention;

FIG. 2 is an axial section of the present invention;

FIG. 3 is a circuit diagram of the present invention;

FIG. 4 is a characteristic graph showing the voltage and current of the ion chambers; and

FIG. 5 is a graph illustrating the voltage and current of both ion chambers.

Referring now to the drawing, and more particularly to FIGS. 1 and 2, a fire detecting device A which detects smoke comprises a housing h and a base 11. The housing h is divided into an inner ion chamber 5 and an outer ion chamber 8, respectively, by an electrode cover 1 having radioactive sources 2 and 3, for instance, such as radium, etc., on both the outer and inner surfaces thereof, contained in the housing h fixed to the base b. The radioactive source 2 located on the inside surface of the electrode cover is covered by the electrode cover 1 and a base plate 4 closes an open end of the cover 1 so that the outer atmosphere is practically isolated from the inner ion chamber 5.

About the outer periphery of the cover 1, an electrode tube 7, having a metal net 6 is disposed, and the electrode tube 7 encloses the outer ion chamber 8 with the radioactive source 3.disposed on the outer surface of the electrode cover 1. Accordingly, the ion chamber 8 is in communication with the outer atmosphere through the metal net 6. The base plate 4 is maintained by a support 5 of a base plate 7' and is substantially made of an insulating material such as, acrylic resin, or any other suitable material, for supporting an inner electrode plate 9 disposed within the inner ion chamber 5.

Referring now again to the drawing, and more particularly to FIG. 3, the electrical circuit is carefully constructed so that the high impedance is not damaged by fixing a field-effect transistor F-ET of high impedance (10 9). A gate electrode of the transistor FET applied as a circuit element in the present device is connected to the electrode cover 1 forming the ion chambers, while drain and source electrodes are respectively operatively connected with the inner electrode plate 9 of the inner ion chamber 5 and a circuit C extending to a receiver R through a potentiometer R Both a resistor R and a condenser ,u. act as circuit protection elements. A circuit C constitutes a testing circuit of a receiver and is connected with the electrode tube 7 of the outer ion chamber 8. The circuit C is for performing an operative test by adjusting the electric voltage of both the inner and outer ion chambers which is effected from the changes in the electric voltage between the circuits N and C through the use of the testing resistor R In accordance with the present invention, the two radioactive sources provided one in each of the outer ion chamber and the inner ion chamber, respectively, always discharge X-rays (alpha rays) in particular directions to- Ward the opposite electrodes. The X-rays ionize the atrnospheric air in chamber 8 and very weak electric current flow between the electrodes 7 and 1, and 9 and 1, the currents being efiected by an electric voltage supplied to the ion chambers.

The current-voltage curve (a) in FIG. 4, shows that an electric current becomes saturated by a certain voltage value.

In this state, if any fine particle appears due to a generation of smoke in the outer ion chamber, the ion current will decrease due to the X-ray being absorbed by the fine particles, or the fine particles absorbing ions, as shown by curve (b) in FIG. 4. This phenomenon will only occur in the outer ion chamber since the smoke is conducted only into the outer ion chamber 8. In this respect a change of voltage-current as shown in FIG. will occur in the series arranged ion chambers 8 and 5. Namely, the current i which flows to the outer ion chamher will decrease to current i, while the voltage v of the outer ion chamber will increase to voltage v The total voltage v across the two ion chambers is always maintained constant and consequently, the voltage change of the outer ion chamber is v '-v =Av. Accordingly, the voltage of the outer ion chamber increases. At this moment, the drain electric current of the transistor FET consequently increases as the voltage between circuits B and C increases as shown in FIG. 3. Therefore, if the electric voltage between circuits C and E becomes larger than the breakdown voltage of the Zener diode D, the rectifier SCR operates as the electric current flows into the gate electrode of the rectifier SCR. In such a state, the signal imparted to the rectifier may accordingly effect operation of an alarm signal by an alarm 10 or lamp 11 connected with the receiver R through a relay device 12, the latter being connected to a battery 13.

An example of the present invention is set forth below.

EXAMPLE A fire detecting device in accordance with the present invention was 114 mm. x 90 mm., and had a total weight of 690 g. (base: 190 g., head 500 g.) and 15 volts D.C. constant circuit voltage. The device was installed at the central portion of a ceiling of 3 meters height and had a fire proof construction. The fire detecting device operated within 30 seconds when a sheet of newspaper of a size of 55 cm. X 82 cm. burned at the corner of the room.

Further, when the same fire detecting device was installed in one corner of the room and the same newspaper was burned at another corner, the detecting device operated within 40 seconds. The room temperature and the humidity at that time were 18 C. and 55%, respectively.

Ten sets of the same fire detecting devices were connected to a receiving set and the maximum consumption of electricity was 4 watts for detection and 6 watts during operation.

Furthermore, with the same fire detecting device, the energy of the X-rays, discharged by Ra was 4.77 mega-electron-volt and the distance traveled up to 32 mm. That is, the outer ion chamber is entirely covered with an effective radiation of X-rays and the space thereof is filled with a uniform disperion of both ion and ion.

In short, in accordance with the present invention, the smoke generated in anticipation of a fire is detected by an ionic phenomenon of radio-active rays and the circuit construction is designed to be operated with a considerably small amount of smoke. The fire detection, accordingly, can be quickly achieved and, in addition, the radioactive soprces which are harmful to the human body are .4 as small as one percent of those of conventional fire detecting devices.

Furthermore, the present device also is remarkably durable due to its simple construction in which a very low constant voltage is applied.

While I have disclosed one embodiment of the present invention, it is to be understood that this embodiment is given by example only.

I claim:

1. An automatic fire detecting device comprising a housing havin openings communicating with the atmosphere,

a dividing means within said housing for dividing said housing into an atmospheric isolated inner ion chamber and an outer ion chamber, said outer ion chamber communicating with the atmosphere and isolated from said inner ion chamber by said dividing means,

said dividing means including an electrode cover having an inner and outer surface communicating with the inner and outer ion chambers, respectively,

an inner radio-active source disposed on said inner surface of said electrode cover,

an outer radio-active source disposed on said outer surface of said electrode cover,

an inner electrode plate disposed in said inner ion chamber in spaced relationship from said inner radioactive source,

an outer electrode means disposed in said outer ion chamber in spaced relationship from said outer radioactive source,

said inner and outer radio-active sources emitting radioactive rays toward said inner electrode plate and said outer electrode means, respectively,

circuit means for comparing the ionization conditions of the inner and outer chambers and detecting any diiference therebetween caused by smoke entering the outer ion chamber,

said circuit means comprising,

a field effect transistor means operative in response to differences in electrical potential across said inner and outer ion chambers caused by changes in the ionization condition of said outer ion chamber upon entrance of smoke therein,

a constant voltage diode means for conducting in response to a predetermined output from said field effect transistor means, and

a controlling rectifier means responsive to the output from said constant voltage diode means.

2. The automatic fire detecting device, as set forth in claim 1, wherein said field eflect transistor means comprises a field effect transistor including a gate end connected to said electrode cover, a drain end connected to said inner electrode plate, and a source end,

a potentiometer having fixed terminals and a variable wiper terminal and said fixed terminals connected between said source end and the negative side of a voltage source,

said constant voltage diode means comprises a Zener diode one terminal of which is connected to said variable wiper terminal of said potentiometer, and

said controlling rectifier means comprises a positive terminal connected to the positive side of said voltage source, and :a negative terminal connected to the negative side of the voltage source, and a gate connected to the other terminal of said Zener diode.

3. The automatic fire detecting device, as set forth in claim 1, wherein said housing and said electrode cover include cylindrical surfaces,

said electrode cover is closed at one end,

a housing base plate enclosing one end of said housing, said housing thereby constituting a cylinder closed at one end, and

said housing and said electrode cover are coaxially disposed in inverted position such that the open end of one faces the closed end of the other.

4. The automatic fire detecting device, as set forth in claim 3, wherein the open end of said electrode cover is outwardly flanged, and

a cover base plate covering said open end of said electrode cover and substantially isolating said inner ion chamber from said outer ion chamber.

5. The automatic fire detecting device, as set forth in claim 3, further comprising a cylindrical base releasably connected to said housing base plate.

6. The automatic fire detecting device, as set forth in claim 4, further comprising a support rod extending coaxially within said housing and secured at one end to said housing base plate and adjacent to the other end supporting said cover base plate.

7. The automatic. fire detecting device, as set forth in 6 claim 6, wherein said support rod supports said inner electrode plate at said other end spaced from said cover base plate.

References Cited UNITED STATES PATENTS JOHN W. CALDWELL, Primary Examiner DANIEL MYER Assistant Examiner US. Cl. X.R. 

